Electric current can produce a magnetic field around a conductor when it flows through a closed circuit. The same current can also heat a conductor because the material resists the flow of electric charge. Cells and batteries produce current through chemical reactions between electrodes and electrolytes.
Electricity shows its presence through visible effects, even when current itself cannot be seen. Important Questions Class 8 Science Chapter 4 help students revise how a current-carrying wire deflects a compass, how a coil becomes an electromagnet, why nichrome wire heats up, and how cells generate current. CBSE 2026 includes magnetic effect of electric current, electromagnets, lifting electromagnets, heating effect, Voltaic cells, dry cells, rechargeable batteries, and battery recycling. Students should practise definitions, reasons, MCQs, and activity-based answers because this chapter tests observation and explanation.
Key Takeaways
- Magnetic Effect: A current-carrying wire produces a magnetic field around it.
- Electromagnet: A current-carrying coil behaves like a magnet while current flows.
- Heating Effect: Resistance converts part of electrical energy into heat energy.
- Battery Safety: Used batteries need e-waste recycling because they contain harmful materials.
Important Questions Class 8 Science Chapter 4 Structure 2026
| Principle |
Application |
Unit |
| Magnetic Effect |
Compass deflection and electromagnets |
Magnetic field |
| Heating Effect |
Heater, iron, kettle, immersion rod |
Heat energy |
| Chemical Cell |
Voltaic cell, dry cell, rechargeable battery |
Electric current |
Important Questions Class 8 Science Chapter 4 With Answers
Important Questions Class 8 Science Chapter 4 begin with the connection between electric current and magnetism. Students must link each observation with the correct scientific reason.
Q1. What Is Magnetic Effect Of Electric Current?
The magnetic effect of electric current is the ability of current to produce a magnetic field around a conductor.
When current flows through a wire, a compass needle kept near it deflects. This happens because the wire behaves like a magnet while current flows through it.
Q2. How Can We Show That Electric Current Has A Magnetic Effect?
We can show it by placing a magnetic compass near a wire connected to a cell and switch.
- Connect a wire to an electric cell and switch.
- Place a compass below the wire.
- Switch the circuit ON.
- The compass needle deflects when current flows.
- The needle returns when the switch is OFF.
Q3. Why Does A Compass Needle Deflect Near A Current-Carrying Wire?
A compass needle deflects because a current-carrying wire produces a magnetic field.
The compass needle is a tiny magnet. When the magnetic field of the wire acts on it, the needle changes direction.
Q4. What Happens To The Compass Needle When Current Stops Flowing?
The compass needle returns to its original direction when current stops flowing.
The magnetic field around the wire disappears when current stops. The compass then aligns again with Earth’s magnetic field.
Q5. Who Discovered The Magnetic Effect Of Electric Current?
Hans Christian Oersted discovered that electric current produces a magnetic effect.
He noticed that a compass needle deflected near a closed electric circuit. His observation proved that electricity and magnetism are linked.
Q6. What Is A Magnetic Field?
A magnetic field is the region around a magnet or current-carrying wire where magnetic effect can be felt.
A compass needle can detect a magnetic field. Its deflection shows that a magnetic effect is present.
Electricity Magnetic And Heating Effects Class 8 Extra Questions With Answers
Electricity Magnetic And Heating Effects Class 8 Extra Questions With Answers help students practise observation-based and application-based answers. These questions follow the NCERT Reprint 2026-27 chapter.
Q7. What Is An Electromagnet?
An electromagnet is a current-carrying coil that behaves like a magnet.
It works only while electric current flows through the coil. An iron nail placed inside the coil makes the electromagnet stronger.
Q8. How Can You Make A Simple Electromagnet?
You can make a simple electromagnet by winding insulated wire around an iron nail and connecting it to a cell.
- Take an iron nail and insulated wire.
- Wrap the wire around the nail in many turns.
- Connect both wire ends to a cell.
- Bring paper clips near the nail.
- The nail attracts clips while current flows.
Q9. Why Does An Electromagnet Stop Attracting Paper Clips When Current Stops?
An electromagnet stops attracting paper clips because its magnetic field disappears when current stops.
The iron nail acts like a magnet only during current flow. This is why an electromagnet is a temporary magnet.
Q10. Why Is An Iron Core Used In An Electromagnet?
An iron core is used because it makes the magnetic field stronger.
A coil without iron can still deflect a compass. A coil with an iron nail can attract more clips because iron strengthens the magnetic effect.
Q11. Does An Electromagnet Have North And South Poles?
Yes, an electromagnet has North and South poles like a bar magnet.
A compass can identify the poles. If the North pole of a compass is attracted to one end, that end is the South pole of the electromagnet.
Q12. How Can The Poles Of An Electromagnet Be Reversed?
The poles of an electromagnet can be reversed by changing the direction of current.
Reversing the battery terminals changes the current direction in the coil. This changes the North and South poles of the electromagnet.
Q13. How Can We Increase The Strength Of An Electromagnet?
We can increase electromagnet strength by increasing current, increasing coil turns, or using an iron core.
More cells provide larger current. More turns of wire strengthen the magnetic field around the coil.
Q14. Where Are Electromagnets Used In Daily Life?
Electromagnets are used in cranes, electric bells, motors, fans, loudspeakers, and scrap yards.
Lifting electromagnets can pick up heavy iron and steel objects. They release the objects when current switches OFF.
Electricity Magnetic And Heating Effects Class 8 Questions With Answers On Electromagnets
Electricity Magnetic And Heating Effects Class 8 Questions With Answers often test the role of current, coil turns, and iron core. Students should explain both observation and reason.
Q15. Why Are Lifting Electromagnets Useful In Factories And Scrap Yards?
Lifting electromagnets are useful because their magnetism can be controlled with a switch.
When current is ON, they lift iron and steel objects. When current is OFF, the magnetic field disappears and the objects fall.
Q16. What Happens If The Iron Nail Is Removed From An Electromagnet?
The coil still produces a magnetic effect, but the effect becomes weaker.
Current flowing through the coil still creates a magnetic field. The iron nail only strengthens the magnetic field.
Q17. Why Does A Battery With Two Cells Make An Electromagnet Stronger Than One Cell?
Two cells usually provide more current than one cell, which makes the electromagnet stronger.
A larger current produces a stronger magnetic field. The electromagnet can then attract more paper clips.
Q18. Why Does Increasing The Number Of Turns Make A Coil Stronger?
Increasing the number of turns strengthens the magnetic field produced by the coil.
Each turn of the coil adds to the magnetic effect. A 100-turn coil attracts more clips than a 25-turn coil with the same cell.
Q19. What Is The Difference Between A Permanent Magnet And An Electromagnet?
A permanent magnet keeps its magnetism, while an electromagnet works only when current flows.
A bar magnet attracts iron without a battery. An electromagnet needs a closed circuit to show magnetic behaviour.
Q20. Why Should An Electromagnet Not Stay Connected To A Cell For Too Long?
An electromagnet should not stay connected too long because the cell can weaken and the wire can heat up.
Continuous current uses the cell’s stored chemical energy. The wire may also become warm due to heating effect.
Q21. Why Does Earth Behave Like A Giant Magnet?
Earth behaves like a giant magnet because movement of liquid iron deep inside Earth can create electric currents.
These currents generate Earth’s magnetic field. A freely suspended magnet aligns in the North-South direction because of this field.
Q22. How Does Earth’s Magnetic Field Help Living Beings?
Earth’s magnetic field helps by shielding Earth from harmful particles from space.
It also helps some migratory birds, fish, and animals navigate. This makes the magnetic field important for life and movement.
Q23. Why Does The Compass Needle Move More When An Iron Nail Is Inside The Coil?
The compass needle moves more because the iron nail strengthens the electromagnet.
The coil’s magnetic field becomes stronger with an iron core. A stronger field causes greater compass deflection.
What Is Heating Effect Of Electric Current Class 8 Questions
What Is Heating Effect Of Electric Current Class 8 questions explain why wires, lamps, and appliances become warm. This concept connects resistance with heat production.
Q24. What Is Heating Effect Of Electric Current?
The heating effect of electric current is the production of heat in a conductor when current flows through it.
A conductor resists the flow of current. Due to this resistance, part of the electrical energy changes into heat energy.
Q25. Why Does Nichrome Wire Become Warm When Current Passes Through It?
Nichrome wire becomes warm because it offers high resistance to current.
High resistance converts more electrical energy into heat. This is why nichrome is used in heating elements.
Q26. Why Is Nichrome Used In Electric Heating Appliances?
Nichrome is used because it produces more heat for a given current than many common conductors.
It also remains stable at high temperatures. Electric heaters, irons, and kettles often use heating elements made from such materials.
Q27. What Factors Affect The Heat Produced In A Wire?
Heat produced in a wire depends on current, wire material, thickness, length, and time of current flow.
A larger current produces more heat. A wire with higher resistance heats more than a low-resistance wire of the same size.
Q28. Why Does A Wire Heat More With Two Cells Than With One Cell?
A wire heats more with two cells because more current flows through it.
More current increases the heating effect. That is why the nichrome wire feels warmer in the two-cell setup.
Q29. Name Some Appliances That Work On Heating Effect Of Electric Current.
Electric heaters, electric stoves, electric kettles, electric irons, immersion rods, and hair dryers work on heating effect.
These appliances contain a heating element. The element becomes hot when current passes through it.
Q30. Why Can Heating Effect Become Dangerous In Household Circuits?
Heating effect can become dangerous because overheating may melt plastic parts or start fires.
Wires, plugs, and sockets must match the current rating. Wrong components can heat too much during use.
Class 8 Science Chapter 4 Extra Questions And Answers On Cells And Batteries
Class 8 Science Chapter 4 Extra Questions And Answers on cells and batteries explain how chemical reactions produce current. Students should learn electrodes, electrolyte, dry cell, and rechargeable battery clearly.
Q31. What Is A Voltaic Cell?
A Voltaic cell is a cell that produces electric current through chemical reactions.
It has two different metal electrodes dipped partly in an electrolyte. It is also called a Galvanic cell.
Q32. What Are Electrodes In An Electric Cell?
Electrodes are conducting rods or strips placed inside a cell.
They are usually made of different materials. In a lemon cell, copper and iron act as electrodes.
Q33. What Is An Electrolyte?
An electrolyte is a liquid or paste that helps a cell produce electric current.
It reacts with the electrodes and allows charge movement. Lemon juice works as an electrolyte in a lemon cell.
Q34. How Does A Lemon Cell Produce Electric Current?
A lemon cell produces current through chemical reactions between lemon juice and two different metals.
- Insert copper and iron into a lemon.
- Keep the metals apart.
- Connect them with wires and an LED.
- The LED glows if current flows correctly.
- Lemon juice acts as the electrolyte.
Q35. Why Does Pure Water Not Work As Well As Lemon Juice In A Cell?
Pure water does not work well because it is a poor electrolyte.
Lemon juice contains acids that help chemical reactions occur. These reactions help current flow through the circuit.
Q36. What Is A Dry Cell?
A dry cell is an electric cell that uses a moist paste instead of a liquid electrolyte.
It has a zinc container as the negative terminal. It also has a carbon rod with a metal cap as the positive terminal.
Q37. Why Is A Dry Cell Convenient For Daily Use?
A dry cell is convenient because it is portable and does not spill liquid electrolyte.
Torches, clocks, remotes, and toys can use dry cells. A dry cell is usually single-use.
Q38. What Are Rechargeable Batteries?
Rechargeable batteries are batteries that can be charged and reused many times.
They are used in phones, laptops, cameras, inverters, and electric vehicles. They reduce wastage compared to many single-use cells.
Q39. Why Do Rechargeable Batteries Wear Out After Many Uses?
Rechargeable batteries wear out because their internal materials slowly change after repeated charging and use.
After many cycles, the battery stores less charge. This is why old phone batteries need charging more often.
Q40. Why Should Used Batteries Be Recycled?
Used batteries should be recycled because they may contain acids and metals harmful to the environment.
Some batteries contain lead, cadmium, nickel, or lithium. Recycling recovers useful materials and reduces pollution.
Class 8 Science Chapter 4 MCQ Questions With Answers
Class 8 Science Chapter 4 MCQ questions test facts, observations, and activity conclusions. Read the explanation after each answer to avoid confusion.
Q41. A Current-Carrying Coil Behaves Like A What?
Answer: Magnet
A current-carrying coil behaves like an electromagnet. Its magnetic effect remains only while current flows.
Q42. Which Material Makes An Electromagnet Stronger?
Answer: Iron
An iron nail inside the coil strengthens the magnetic field. Paper, plastic, and wood do not create the same effect.
Q43. Why Is Nichrome Wire Used In Heating Devices?
Answer: It generates more heat for a given current.
Nichrome has high resistance. This helps electrical energy change into heat energy.
Q44. What Happens To A Compass Near A Current-Carrying Wire?
Answer: The compass needle deflects.
The wire produces a magnetic field when current flows. The compass needle responds to this field.
Q45. Which Device Works On Heating Effect Of Electric Current?
Answer: Electric iron
An electric iron has a heating element. Current heats the element and warms the iron plate.
Q46. Which Device Works On Magnetic Effect Of Electric Current?
Answer: Electromagnet
An electromagnet uses current in a coil to produce magnetism. It loses magnetism when current stops.
Q47. What Is The Electrolyte In A Lemon Cell?
Answer: Lemon juice
Lemon juice helps chemical reactions occur between two different metals. This helps the cell produce current.
Q48. Can A Usual Dry Cell Be Recharged After It Is Used Up?
Answer: No
A usual dry cell is a single-use cell. Rechargeable batteries are designed differently.
Class 8 Science Chapter 4 Case Study Questions With Answers
Class 8 Science Chapter 4 Case Study Questions help students apply concepts to activity-based situations. These answers explain the observation, reason, and conclusion.
Q49. Sumana’s Lifting Electromagnet Stops Lifting Clips, But The Wire Is Still Warm. Why?
The electromagnet may stop lifting clips because the cell has weakened after continuous current flow.
A weak cell may not provide enough current to produce a strong magnetic field. The warm wire shows that current flowed for some time and caused heating.
Q50. Neha Removes The Iron Nail From The Coil. Will The Compass Still Deflect?
Yes, the compass will still deflect, but the deflection will be smaller.
The current-carrying coil still produces a magnetic field. The iron nail only increases the strength of the electromagnet.
Q51. In Which Lemon Cell Case Will The LED Glow: Lemon Juice Or Pure Water?
The LED is more likely to glow with lemon juice.
Lemon juice acts as a better electrolyte than pure water. It helps chemical reactions occur between the copper and iron electrodes.
Q52. Will Compass Needles Deflect Near Coils Made Of Iron, Copper, Aluminium, And Nichrome?
Yes, compass needles can deflect near all four coils if current flows through them.
The magnetic effect depends mainly on current flow through the conductor. The material can affect resistance and heating, but current still produces a magnetic field.
Electricity Magnetic And Heating Effects Class 8 Worksheet Questions
Electricity Magnetic And Heating Effects Class 8 Worksheet Questions help students revise fill-in-the-blanks, true or false, and activity-based answers. This section covers electrolyte, electromagnets, current direction, nichrome wire, and rechargeable batteries.
Q53. Fill In The Blank: The Solution Used In A Voltaic Cell Is Called ______.
The solution used in a Voltaic cell is called an electrolyte.
An electrolyte is the liquid or paste that helps chemical reactions occur inside a cell. In a lemon cell, lemon juice acts as the electrolyte because it helps current flow between two different metals.
Q54. Fill In The Blank: A Current-Carrying Coil Behaves Like A ______.
A current-carrying coil behaves like a magnet.
When current flows through the coil, it produces a magnetic field around it. If an iron nail is placed inside the coil, the magnetic field becomes stronger and the coil works as an electromagnet.
Q55. True Or False: A Coil Becomes An Electromagnet Only When Current Flows Through It.
True.
A coil becomes an electromagnet only when electric current flows through it. When the switch is turned OFF, current stops and the coil loses its magnetic effect.
Q56. True Or False: An Electromagnet With One Cell Attracts More Clips Than The Same One With Two Cells.
False.
An electromagnet with two cells usually attracts more clips than the same electromagnet with one cell. Two cells provide a larger current, which produces a stronger magnetic field around the coil.
Q57. Why Are Electric Heating Devices Convenient Compared To Firewood Or Charcoal?
Electric heating devices are convenient because they produce heat without burning fuel at the place of use.
They reduce smoke, ash, and soot inside homes. Devices such as electric irons, kettles, and room heaters also give controlled heating through a heating element.
Q58. What Happens If Battery Terminals Are Reversed In An Electromagnet Circuit?
The poles of the electromagnet get reversed when battery terminals are reversed.
Reversing the terminals changes the direction of current through the coil. Since the magnetic field depends on current direction, the North and South poles interchange.
Q59. Why Does An Incandescent Lamp Become Warm?
An incandescent lamp becomes warm because current heats its filament.
The filament offers resistance to electric current. This resistance converts part of the electrical energy into heat and light.
Q60. Why Do Rechargeable Batteries Wear Out After Many Uses?
Rechargeable batteries wear out because their internal materials slowly change after repeated charging and use.
After many charge-discharge cycles, the battery holds less charge than before. This is why old mobile phone batteries need charging more often.
Class 8 Science Chapter List